Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A method of applying a pattern of metal, metal oxide, and/or
semiconductor material on a substrate, a pattern created by that method,
and uses of that pattern.

Claims:

1. A method of applying a pattern of metal, metal oxide and/or
semiconductor material on a substrate, comprising: a) providing a first
substrate, b) creating a pattern of metal, metal oxide and/or
semiconductor material on said first substrate, c) providing a second
substrate and bringing it into conformal contact with said pattern of
metal, metal oxide and/or semiconductor material on said first substrate,
d) separating said second substrate from said first substrate, thus
having said pattern of metal, metal oxide and/or semiconductor material
adhere to said second substrate and being separated together with said
second substrate from said first substrate.

2. The method according to claim 1, wherein b) is performed by the
following sequence: ba) creating a resist pattern on said first
substrate, bb) applying a layer of metal, metal oxide and/or
semiconductor material on said first substrate having said resist pattern
on it, bc) removing said resist pattern from said first substrate to
leave behind a pattern of metal, metal oxide and/or semiconductor
material on said first substrate.

3. The method according to claim 1, wherein b) is performed by the
following sequence: ba) applying a layer of metal, metal oxide and/or
semiconductor material on said first substrate, bb) creating a resist
pattern on said first substrate having said layer of metal on it, bc)
removing said layer of metal, metal oxide and/or semiconductor material
in positions which are not covered by said resist pattern, by means of an
etching technique, bd) removing said resist pattern from said first
substrate to leave behind a pattern of metal, metal oxide and/or
semiconductor material on said first substrate.

4. The method according to claim 1, wherein b) is performed by: ba)
applying a layer of metal, metal oxide and/or semiconductor material on
said first substrate by using a patterned mask through which said metal,
metal oxide and/or semiconductor material is applied such that said layer
of metal, metal oxide and semiconductor material becomes patterned.

5. The method according to claim 1, wherein said resist pattern on said
first substrate comprises positions having resist present on said first
substrate and positions having no resist present on said first substrate.

6. The method according to claim 2, wherein in bb), said layer of metal,
metal oxide and/or semiconductor material is applied on said first
substrate on said resist pattern both in said positions having resist
present and in said positions having no resist present.

7. The method according to claim 2, wherein said layer of metal, metal
oxide and/or semiconductor material is applied as a continuous layer.

8. The method according to claim 2, wherein said pattern of metal, metal
oxide and/or semiconductor material created by b), comprises positions
having metal, metal oxide and/or semiconductor material present on said
first substrate and positions having no metal, metal oxide and/or
semiconductor material present on said first substrate, and said
positions of said pattern of metal, metal oxide and/or semiconductor
material having metal, metal oxide and/or semiconductor material present
on said first substrate coincide with positions of said resist pattern of
ba) where there is no resist present on said first substrate in ba).

9. The method according to claim 3, wherein said pattern of metal, metal
oxide and/or semiconductor material created by b), comprises positions
having metal, metal oxide and/or semiconductor material present on said
first substrate and positions having no metal, metal oxide and/or
semiconductor material present on said first substrate, and said
positions of said pattern of metal, metal oxide and/or semiconductor
material having metal, metal oxide and/or semiconductor material present
on said first substrate coincide with positions of said resist pattern of
bb) where there is resist present on said first substrate in bb).

10. The method according to claim 2, wherein said resist pattern is
created by a lithographic process, preferably by a lithographic process
selected from the group comprising optical lithography, electron beam
lithography, soft lithography, UV-nanoimprint lithography and nanoimprint
lithography.

11. The method according to claim 2, wherein said layer of metal, metal
oxide and/or semiconductor material is applied on said first substrate by
a process selected form the group comprising vapour deposition,
sputtering, evaporation, wet chemical deposition, plating and
selfassembly.

12. The method according to claim 2, wherein the removing of said resist
pattern occurs by dissolving said resist pattern in a solvent, such
acetone, isopropanol, N-pyrrolidone, and special resist removers, such as
AZ-remover, and any combination thereof.

13. The method according to claim 1, wherein said first substrate is made
of a material selected from the group comprising single crystalline
materials, polycrystalline materials, materials such as GaAs, Si,
SiO2, mica, amorphous composites, such as glass and float glass, and
perovskites.

14. The method according to claim 1, wherein said metal is select from
the group comprising Au, Ti, Pt, Ag, Cr, Cu, Al, said metal oxide is
selected from the group comprising Al2O3, AgO, TiO2,
SiO2, DyScO3, yttria stabilized zirconia (YSZ), and said
semiconductor material is selected from the group comprising Si, Ge,
GaAs, GaN, InSb, InP, CdS, ZnSe.

15. The method according to claim 2, wherein said layer of metal, metal
oxide and/or semiconductor material is applied directly on said first
substrate or, if present, on said resist pattern on said first substrate,
without a layer of lubricant being present on or having been previously
applied to said first substrate or, if present, on said resist pattern on
said first substrate, said layer of metal, metal oxide and/or
semiconductor material after application thus being in direct contact
with said first substrate and/or said resist pattern.

16. The method according to claim 2, wherein ba) is performed in the
following manner: ba) creating a resist pattern on said first substrate
and thereafter applying a layer of lubricant to said resist pattern on
said first substrate to weaken the adhesion between said pattern of
metal, metal oxide and/or semiconductor material and said first substrate
having a resist pattern on it.

17. The method according to claim 3, wherein ba) is performed in the
following manner: ba) applying a layer of lubricant to said first
substrate and thereafter applying a layer of metal, metal oxide and/or
semiconductor material to said first substrate having a layer of
lubricant on it, said layer of lubricant serving the purpose of weakening
the adhesion between said pattern of metal, metal oxide and/or
semiconductor material and said first substrate.

18. The method according to claim 4, wherein ba) is performed in the
following manner: ba) applying a layer of lubricant to said first
substrate and thereafter applying a layer of metal, metal oxide and/or
semiconductor material to said first substrate having a layer of
lubricant on it, said layer of lubricant serving the purpose of weakening
the adhesion between said pattern of metal, metal oxide and/or
semiconductor material and said first substrate.

19. The method according to claim 16, wherein said lubricant is selected
from the group comprising fluorosilanes, such as
perfluoro-alkyltrichlorosilane C4F8, silane derivatives with a
CH3 terminus, teflon and teflon-like materials.

20. The method according to claim 16, wherein in ba) said layer of
lubricant is applied to said resist pattern on said first substrate,
wherein, after subsequently removing said resist pattern in bc), said
layer of lubricant is only present in said positions having no resist
present.

21. The method according to claim 20, wherein in bb), said layer of
metal, metal oxide and/or semiconductor material is applied on said first
substrate having a resist pattern on it, such that it is in direct
contact with said resist pattern in positions having resist present and
in direct contact with said lubricant in positions having no resist
present.

22. The method according to claim 1, wherein after said pattern of metal,
metal oxide and/or semiconductor material has been created in b) on said
first substrate, a transfermediating layer is applied to said pattern of
metal, metal oxide and/or semiconductor material prior to c), which
transfermediating layer serves the purpose of mediating adhesion between
said pattern of metal, metal oxide and/or semiconductor material and said
second substrate.

23. The method according to claim 22, wherein said transfermediating
layer is made of a material comprising a compound having at least two
termini, wherein one terminus is a metal binding, metal oxide binding or
semiconductor binding group, such as thiol, and the other terminus
provides controllable adhesion to said second substrate.

24. The method according to claim 23, wherein said transfermediating
layer is providing controllable adhesion by comprising at least one
compound having polar groups for interaction with a hydrophilic solvent,
said compound preferably forming a self-assembled monolayer, such as an
alkanethiol, or said transfer mediating layer is soluble in water, such
as a layer of CaO.

25. The method according to claim 1, wherein said second substrate is
made of a polymeric material, preferably a polymeric material selected
from the group comprising elastomers, plastomers, ionomers and resists.

26. The method according to claim 1, wherein during or after c) and
before d), said second substrate and said pattern of metal, metal oxide
and/or semiconductor material on said first substrate, whilst being in
conformal contact with each other, are exposed or placed into a polar
solvent to weaken the adhesion between said pattern of metal, metal oxide
and/or semiconductor material and said first substrate.

27. The method according to claim 26, wherein said polar solvent is
selected from the group of organic and inorganic polar solvents and
mixtures thereof, preferably from the group comprising water,
isopropanol, ethanol, methanol, acetone, dimethylsulfoxide and
acetonitrile, and mixtures thereof.

28. The method according to claim 26, wherein said solvent does not have
any added solutes dissolved in said solvent.

29. The method according to claim 1, wherein after b) and before c), said
pattern of metal, metal oxide and/or semiconductor material on said first
substrate is placed in a solution of a surfactant and, optionally,
subsequently rinsed.

30. The method according to claim 29, wherein said surfactant is selected
from the group comprising dithiocarbamate derivatives formed from alkane
chains with primary amines, and the solvent wherein said surfactant is
dissolved is selected from the group comprising isopropanol, ethanol,
water and mixtures thereof.

31. The method according to claim 1, further comprising: e1) providing a
third substrate, bringing it into conformal contact with said second
substrate having said pattern of metal, metal oxide and/or semiconductor
material on it, and separating said second substrate from said third
substrate, thus having said pattern of metal, metal oxide and/or
semiconductor material adhere to said third substrate and being separated
together with said third substrate from said second substrate.

32. The method according to claim 31, wherein said third substrate has
functional groups allowing a transfer of said pattern of metal, metal
oxide and/or semiconductor material from said second substrate to said
third substrate, such as mercapto groups or amino groups on it.

33. The method according to claim 31, wherein said third substrate, prior
to e1) has a further pattern of metal, metal oxide and/or semiconductor
material on its surface, and/or an additional layer on it providing
functionality, and/or is covered with nanowires, nanocolumns, carbon
nanotubes, and/or has switchable oxides, such as TiO2 or perovskites
on it.

34. The method according to claim 1, further comprising: e2) using said
second substrate having said pattern of metal, metal oxide and/or
semiconductor materials adhered to it for the preparation of a flexible
organic electronic device, such as an organic light emitting diode
(OLED), an organic field effect transistor (OFET), a molecular electronic
device or a sensor device, preferably by laminating said second substrate
to another substrate and thereby sandwiching said pattern of metal, metal
oxide and/or semiconductor material between the two substrates.

35. The method according to claim 1, wherein said pattern of metal, metal
oxide and/or semiconductor material has an adhesion force to said first,
second and, if present, third substrate, wherein the adhesion force to
said third substrate is greater than the adhesion force to said second
substrate which is greater than the adhesion force to said first
substrate.

36. The method according to claim 35, wherein said pattern of metal,
metal oxide and/or semiconductor material is a pattern of gold, said
first substrate is Si, with or without an oxide layer on it, or mica, or
glass, said second substrate is a polyolefine plastomer (POP) or
polydimethylsiloxane (PDMS), or a ionomer such as Surlyn, and said third
substrate, if present, is Si, mica, or glass, which is optionally
functionalized with functional groups, to allow adhesion of said pattern
of gold on it.

37. The method according to claim 36, wherein said functionalizing occurs
by using compounds having mercapto groups or amino groups or carboxy
groups, preferably dendrimer compounds.

38. The method according to claim 1, wherein e1) is performed in the
absence of any additional layer providing functionality on said third
substrate.

39. The method according to claim 38, wherein e1) is performed by
weakening the adhesion forces between said second substrate and said
pattern of metal, metal oxide and/or semiconductor material by exposing
said second substrate and said pattern of metal, metal oxide and/or
semiconductor material on it to a solvent or placing it into a solvent
such as isopropanol, ethanol, methanol, propanol and hexane.

40. The method according to claim 31, wherein e1) is performed by
weakening the adhesion forces between said second substrate and said
pattern of metal, metal oxide and/or semiconductor material by placing a
solvent between said second substrate having said pattern of metal, metal
oxide and/or semiconductor material on it and said third substrate, and
thereby increasing the adhesion forces between said third substrate and
said pattern of metal, metal oxide and/or semiconductor material or, if
present, between said transfer mediating layer on said third substrate
and said pattern of metal, metal oxide and/or semiconductor material.

41. The method according to claim 1, wherein second substrate is prepared
by a method selected from the group comprising drop casting, curing,
preferably thermo or photo induced curing, and hot embossing.

42. The method according to claim 1, wherein said second substrate has a
flat surface which, in c), said pattern of metal, metal oxide, and/or
semiconductor material is brought into conformal contact with

43. The method according to claim 42, wherein said second substrate has a
stabilizing hard back plane opposite said flat surface.

44. The method according to claim 1, wherein said bringing into conformal
contact in c) and e1) occurs for a period in the range of from 1 s-120
min.

45. The method according to claim 1, wherein said bringing into conformal
contact in c) and e1) is a pressing process with an average pressure of 1
mbar-5 bar.

46. A pattern of metal, metal oxide and/or semiconductor material on a
substrate produced by the method according to claim 1.

47. The pattern according to claim 46, having no defects or artifacts in
said pattern.

48. Use of the pattern according to claim 46 in an electronic device,
polymeric device, biomedical device.

Description:

[0001] The present application relates to a method of applying a pattern
of metal, metal oxide and/or semiconductor material on a substrate, to a
pattern created by such method and to uses of such pattern.

[0002] During the past decade, soft lithography has developed to a
versatile technique for fabricating chemically micro- and nanostructured
surfaces [1,2]. Among several techniques known collectively as soft
lithography, micro contact printing (μCP) has become the most commonly
used method [1]. The technique was initially developed for the transfer
of molecules and was also applied for the transfer of metals [3].

[0003] Two soft-lithographic methods for contacting organic materials with
metals have been developed up to now, namely nanotransfer printing (nTP)
[4,5] and soft-contact lamination (ScL) [6]. They can be used for the
parallel fabrication of multiple devices. Both methods are schematically
depicted in FIG. 1.

[0004] In case of nTP (FIG. 1a), a thin layer of metal is evaporated onto
a patterned elastomeric stamp, which has been fabricated by drop casting
of polydimethylsiloxane (PDMS) onto a patterned Si wafer. The evaporated
metal layer is brought into conformal contact with an organic layer on a
substrate. As a result of the chemical bond formation at the
metal-organic interface, the metal-organic adhesion is stronger than the
metal-PDMS adhesion and the metal layer is transferred from the PDMS
stamp onto the organic layer. The process takes place under ambient
conditions without application of any additional pressure. This process
has been demonstrated by the fabrication of Au top electrodes in
Au/alkanedithiol/GaAs hetero junctions [7] and Au/mercaptosilane/Si
hetero junctions [8]. In another process gold was patterned on Silicon
wafers and subsequently transferred to selected polymers at high pressure
(9-30 bar) and temperature between 100 and 140° C. [9].

[0005] In case of ScL the metal-organic adhesion is based on van der Waals
interactions and weaker than the metal-PDMS interaction. Thus in this
process the metal is not transferred from the PDMS onto the organic
layer, but the PDMS remains on the Au layer and is part of the
PDMS/metal/organic/substrate hetero junction (FIG. 1b). The metal layer
is prepared on top of an unstructured flat PDMS layer using shadow mask
evaporation. The process takes place under ambient conditions without
application of any additional pressure [10].

[0006] Both processes, however, are not scalable to critical dimensions
below 50 nm. In case of ScL the scaling of the process is difficult since
the metal structures are defined on a flat stamp by using a shadow mask
evaporation technique. In case of nTP the critical dimensions for the
transfer are limited by the properties of the stamps:

[0007] The stamp material should not be too hard, so that the transfer
across step edges is possible.

[0008] The aspect ratio of the structures in the stamps has to be
optimized with respect to buckling, lateral collapse and roof collapse.

[0009] The evaporation of Au onto the structured stamp is critically
dependent on the angle of evaporation and on the aspect ratio of the
stamp.

[0010] The transfer of the Au layer from the stamp onto the substrate at
the contact area requires a destruction of the homogeneous Au layer on
the stamp surface. The disruption of the Au layer can lead to rough
edges.

[0011] In addition to the above described processes, it is also possible
to directly evaporate metals in patterns or without patterns onto
molecular layers immobilized onto substrates. However, it is known that
it is difficult to avoid the diffusion of metal atoms into the molecular
layers. These atoms can easily lead to the formation of e.g. filaments,
that dominate the I-V characteristic across the molecular layers. For
GaAs/Dithiol/Au junctions it was shown [11] that evaporation of Au onto
monolayers of dithiol derivatives, unavoidably leads to direct contacts
between GaAs and the evaporated gold. These "shorts" dominate the IV
characteristics. In case of nTP none of these direct contacts were found.

[0012] None of the aforementioned techniques could be scaled down to
dimensions as low as 50-100 nm. Moreover, it has not been possible to
prepare patterns having a surface roughness in the nm-range, nor was it
possible to create patterns that had smooth edges.

[0013] Accordingly, it was an object of the present invention to provide
for a fabrication process which can be scaled down to dimensions as low
as 50-100 nm which fabrication process is easy to perform and versatile
with respect to different metals, metal oxides and semiconductor
materials. It has furthermore been an object of the present invention to
provide for a process allowing the fabrication of patterns having smooth
edges and a mean surface roughness ≦2 nm. The objects of the
present invention are solved by a method of applying a pattern of metal,
metal oxide and/or semiconductor material on a substrate, comprising the
steps: [0014] a) providing a first substrate, [0015] b) creating a
pattern of metal, metal oxide and/or semiconductor material on said first
substrate, [0016] c) providing a second substrate and bringing it into
conformal contact with said pattern of metal, metal oxide and/or
semiconductor material on said first substrate, [0017] d) separating said
second substrate from said first substrate, thus having said pattern of
metal, metal oxide and/or semiconductor material adhere to said second
substrate and being separated together with said second substrate from
said first substrate.

[0018] In one embodiment step b) is performed by the following sequence of
steps: [0019] ba) creating a resist pattern on said first substrate,
[0020] bb) applying a layer of metal, metal oxide and/or semiconductor
material on said first substrate having said resist pattern on it, [0021]
bc) removing said resist pattern from said first substrate to leave
behind a pattern of metal, metal oxide and/or semiconductor material on
said first substrate.

[0022] In another embodiment step b) is performed by the following
sequence of steps: [0023] ba) applying a layer of metal, metal oxide
and/or semiconductor material on said first substrate, [0024] bb)
creating a resist pattern on said first substrate having said layer of
metal on it, [0025] bc) removing said layer of metal, metal oxide and/or
semiconductor material in positions which are not covered by said resist
pattern, by means of an etching technique, [0026] bd) removing said
resist pattern from said first substrate to leave behind a pattern of
metal, metal oxide and/or semiconductor material on said first substrate.

[0027] In yet another embodiment step b) is performed by the following
steps: [0028] ba) applying a layer of metal, metal oxide and/or
semiconductor material on said first substrate by using a patterned mask
through which said metal, metal oxide and/or semiconductor material is
applied such that said layer of metal, metal oxide and semi-conductor
material becomes patterned.

[0029] In the embodiments, involving a resist pattern, said resist pattern
on said first substrate preferably, comprises positions having resist
present on said first substrate and positions having no resist present on
said first substrate.

[0030] In the embodiments, wherein the resist pattern is first created and
subsequently a layer of metal oxide and/or semiconductor material is
applied ("resist first" embodiment), preferably, in step bb), said layer
of metal, metal oxide and/or semiconductor material is applied on said
first substrate on said resist pattern both in said positions having
resist present and in said positions having no resist present.

[0031] In one embodiment, said layer of metal, metal oxide and/or
semiconductor material is applied as a continuous layer.

[0032] In the "resist first" embodiment, preferably, said pattern of
metal, metal oxide and/or semi-conductor material created by step b),
comprises positions having metal, metal oxide and/or semiconductor
material present on said first substrate and positions having no metal,
metal oxide and/or semiconductor material present on said first
substrate, and said positions of said pattern of metal, metal oxide
and/or semiconductor material having metal, metal oxide and/or
semiconductor material present on said first substrate coincide with
positions of said resist pattern of step ba) where there is no resist
present on said first substrate in step ba).

[0033] In the embodiment, wherein first layer of metal, metal oxide and/or
semiconductor material is applied and subsequently a resist pattern is
created ("resist second" embodiment), it is preferred that said pattern
of metal, metal oxide and/or semiconductor material created by step b),
comprises positions having metal, metal oxide and/or semiconductor
material present on said first substrate and positions having no metal,
metal oxide and/or semiconductor material present on said first
substrate, and said positions of said pattern of metal, metal oxide
and/or semiconductor material having metal, metal oxide and/or
semiconductor material present on said first substrate coincide with
positions of said resist pattern of step bb) where there is resist
present on said first substrate in step bb).

[0034] In the embodiments, involving a resist pattern, said resist pattern
is, preferably, created by a lithographic process, preferably by a
lithographic process selected from the group comprising optical
lithography, electron beam lithography, soft lithography, UV-nanoimprint
lithography and nanoimprint lithography.

[0035] Preferably, said layer of metal, metal oxide and/or semiconductor
material is applied on said first substrate by a process selected form
the group comprising vapour deposition, sputtering, evaporation, wet
chemical deposition, plating and self-assembly.

[0036] In the embodiments, involving a resist pattern, the removing of
said resist pattern preferably occurs by dissolving said resist pattern
in a solvent, such acetone, isopropanol, N-pyrrolidone, and special
resist removers, such as AZ-remover, and any combination thereof.

[0037] Preferably, said first substrate is made of a material selected
from the group comprising single crystalline materials, polycrystalline
materials, materials such as GaAs, Si, SiO2, mica, amorphous
composites, such as glass and float glass, and perovskites.

[0038] Preferably, said metal is select from the group comprising Au, Ti,
Pt, Ag, Cr, Cu, Al, said metal oxide is selected from the group
comprising Al2O3, AgO, TiO2, SiO2, DyScO3,
yttria stabilized zirconia (YSZ), and said semiconductor material is
selected from the group comprising Si, Ge, GaAs, GaN, InSb, InP, CdS,
ZnSe.

[0039] In one embodiment, said layer of metal, metal oxide and/or
semiconductor material is applied directly on said first substrate or, if
present, on said resist pattern on said first substrate, without a layer
of lubricant being present on or having been previously applied to said
first substrate or, if present, on said resist pattern on said first
substrate, said layer of metal, metal oxide and/or semiconductor material
after application thus being in direct contact with said first substrate
and/or said resist pattern.

[0040] Preferably, in the "resist first" embodiment, step ba) is performed
in the following manner: [0041] ba) creating a resist pattern on said
first substrate and thereafter applying a layer of lubricant to said
resist pattern on said first substrate to weaken the adhesion between
said pattern of metal, metal oxide and/or semiconductor material and said
first substrate having a resist pattern on it.

[0042] Preferably, in the "resist second" embodiment, step ba) is
performed in the following manner: [0043] ba) applying a layer of
lubricant to said first substrate and thereafter applying a layer of
metal, metal oxide and/or semiconductor material to said first substrate
having a layer of lubricant on it, said layer of lubricant serving the
purpose of weakening the adhesion between said pattern of metal, metal
oxide and/or semiconductor material and said first substrate.

[0044] Preferably, in the embodiment involving no resist, step ba) is
performed in the following manner: [0045] ba) applying a layer of
lubricant to said first substrate and thereafter applying a layer of
metal, metal oxide and/or semiconductor material to said first substrate
having a layer of lubricant on it, said layer of lubricant serving the
purpose of weakening the adhesion between said pattern of metal, metal
oxide and/or semiconductor material and said first substrate.

[0046] Preferably, said lubricant is selected from the group comprising
fluorosilanes, such as perfluoro-alkyltrichlorosilane C4F8,
silane derivatives with a CH3 terminus, teflon and teflon-like
materials.

[0047] Preferably, in the "resist first" embodiment, in step ba) said
layer of lubricant is applied to said resist pattern on said first
substrate , wherein, after subsequently removing said resist pattern in
step bc), said layer of lubricant is only present in said positions
having no resist present.

[0048] More preferably in step bb), said layer of metal, metal oxide
and/or semiconductor material is applied on said first substrate having a
resist pattern on it, such that it is in direct contact with said resist
pattern in positions having resist present and in direct contact with
said lubricant in positions having no resist present.

[0049] In one embodiment, after said pattern of metal, metal oxide and/or
semiconductor material has been created in step b) on said first
substrate, a transfer-mediating layer is applied to said pattern of
metal, metal oxide and/or semiconductor material prior to step c), which
transfer-mediating layer serves the purpose of mediating adhesion between
said pattern of metal, metal oxide and/or semiconductor material and said
second substrate, wherein, preferably, said transfer-mediating layer is
made of a material comprising a compound having at least two termini,
wherein one terminus is a metal binding, metal oxide binding or
semiconductor binding group, such as thiol, and the other terminus
provides controllable adhesion to said second substrate.

[0050] Such controllability may, for example, be achieved by appropriate
choice of solvent which interacts with said terminus.

[0051] More preferably, said transfer-mediating layer is providing
controllable adhesion by comprising at least one compound having polar
groups for interaction with a hydrophilic solvent, said compound
preferably forming a self-assembled monolayer, such as an alkanethiol, or
said transfer mediating layer is soluble in water, such as a layer of
CaO.

[0052] In one embodiment said second substrate is made of a polymeric
material, preferably a polymeric material selected from the group
comprising elastomers, plastomers, ionomers and resists.

[0053] In one embodiment during or after step c) and before step d), said
second substrate and said pattern of metal, metal oxide and/or
semiconductor material on said first substrate, whilst being in conformal
contact with each other, are exposed or placed into a polar solvent to
weaken the adhesion between said pattern of metal, metal oxide and/or
semiconductor material and said first substrate, wherein, preferably said
polar solvent is selected from the group of organic and inorganic polar
solvents and mixtures thereof, preferably from the group comprising
water, isopropanol, ethanol, methanol, acetone, dimethylsulfoxide and
acetonitrile, and mixtures thereof.

[0054] Preferably, said solvent does not have any added solutes dissolved
in said solvent.

[0055] "Added solutes", as used herein, is meant to signify that said
solvent does not contain any solutes which have been specifically added
to it, e.g. by the experimentator or the manufacturer. "Added solutes",
however, does not exclude the presence of dissolved impurities or
dissolved gasses or humidity.

[0056] In another embodiment after step b) and before step c), said
pattern of metal, metal oxide and/or semiconductor material on said first
substrate is placed in a solution of a surfactant and, optionally,
subsequently rinsed, wherein, preferably said surfactant is selected from
the group comprising dithiocarbamate derivatives formed from alkane
chains with primary amines, and the solvent wherein said surfactant is
dissolved is selected from the group comprising isopropanol, ethanol,
water and mixtures thereof.

[0057] In one embodiment said method comprises the additional step:
[0058] e1) providing a third substrate, bringing it into conformal
contact with said second substrate having said pattern of metal, metal
oxide and/or semiconductor material on it, and separating said second
substrate from said third substrate, thus having said pattern of metal,
metal oxide and/or semiconductor material adhere to said third substrate
and being separated together with said third substrate from said second
substrate.

[0059] Preferably, said third substrate has functional groups allowing a
transfer of said pattern of metal, metal oxide and/or semiconductor
material from said second substrate to said third substrate, such as
mercapto groups or amino groups on it.

[0060] In one embodiment said third substrate, prior to step e1) has a
further pattern of metal, metal oxide and/or semiconductor material on
its surface, and/or an additional layer on it providing functionality,
and/or is covered with nanowires, nanocolumns, carbon nanotubes, and/or
has switchable oxides, such as TiO2 or perovskites on it.

[0061] In one embodiment said method comprises the additional step:
[0062] e2) using said second substrate having said pattern of metal,
metal oxide and/or semi-conductor materials adhered to it for the
preparation of a flexible organic electronic device, such as an organic
light emitting diode (OLED), an organic field effect transistor (OFET), a
molecular electronic device or a sensor device, preferably by laminating
said second substrate to another substrate and thereby sandwiching said
pattern of metal, metal oxide and/or semiconductor material between the
two substrates.

[0063] In one embodiment said pattern of metal, metal oxide and/or
semiconductor material has an adhesion force to said first, second and,
if present, third substrate, wherein the adhesion force to said third
substrate is greater than the adhesion force to said second substrate
which is greater than the adhesion force to said first substrate.

[0064] Preferably, said pattern of metal, metal oxide and/or semiconductor
material is a pattern of gold, said first substrate is Si, with or
without an oxide layer on it, or mica, or glass, said second substrate is
a polyolefine plastomer (POP) or polydimethylsiloxane (PDMS), or a
ionomer such as Surlyn, and said third substrate, if present, is Si,
mica, or glass, which is optionally functionalized with functional
groups, to allow adhesion of said pattern of gold on it.

[0065] More preferably, said functionalizing occurs by using compounds
having mercapto groups or amino groups or carboxy groups, preferably
dendrimer compounds.

[0066] In one embodiment step e1) is performed in the absence of any
additional layer providing functionality on said third substrate,
wherein, preferably, step e1) is performed by weakening the adhesion
forces between said second substrate and said pattern of metal, metal
oxide and/or semiconductor material by exposing said second substrate and
said pattern of metal, metal oxide and/or semiconductor material on it to
a solvent or placing it into a solvent such as isopropanol, ethanol,
methanol, propanol and hexane.

[0067] In another embodiment step e1) is performed by weakening the
adhesion forces between said second substrate and said pattern of metal,
metal oxide and/or semiconductor material by placing a solvent between
said second substrate having said pattern of metal, metal oxide and/or
semiconductor material on it and said third substrate, and thereby
increasing the adhesion forces between said third substrate and said
pattern of metal, metal oxide and/or semi-conductor material or, if
present, between said transfer mediating layer on said third substrate
and said pattern of metal, metal oxide and/or semiconductor material.

[0068] In one embodiment said second substrate is prepared by a method
selected from the group comprising drop casting, curing, preferably
thermo- or photo induced curing, and hot embossing.

[0069] Preferably, said second substrate has a flat surface which, in step
c), said pattern of metal, metal oxide, and/or semiconductor material is
brought into conformal contact with

[0070] More preferably, said second substrate has a stabilizing hard back
plane opposite said flat surface.

[0071] In one embodiment said bringing into conformal contact in steps c)
and e1) occurs for a period in the range of from 1 s-120 min.

[0072] In one embodiment said bringing into conformal contact in steps c)
and e1) is a pressing process with an average pressure of 1 mbar-5 bar.

[0073] The objects of the present invention are also solved by a pattern
of metal, metal oxide and/or semiconductor material on a substrate
produced by the method according to the present invention.

[0074] Preferably, said pattern has no defects or artifacts in said
pattern.

[0075] The objects of the present invention are also solved by a use of
the pattern according to the present invention in an electronic device,
polymeric device, biomedical device.

[0076] As used herein, the term "to bring a substrate into conformal
contact with a pattern of metal, metal oxide and/or semiconductor
material", is meant to denote any contact between said substrate and said
pattern allowing the transfer of said pattern to said substrate. In some
embodiments, exertion of pressure is needed for such transfer to occur,
and in these instances, the term "to bring into conformal contact with"
is to be equated with "to press on (to)".

[0077] Resists useful for the purposes of the present invention are well
known to someone skilled in the art. Exemplary resists useful for the
purposes of the present invention are photoresists, electron-beam
resists, x-ray-resists, nanoimprint resists etc. More specific examples
of resists useful for the present invention are PMMA (electron-beam), AZ
5214 (photo), NXR2010-3020 (nanoimprint) or others.

[0078] Sometimes, in the present application reference is made to bringing
one substrate into conformal contact with a pattern of metal on another
substrate and subsequently "separating" the one substrate from the other
substrate. This process of separating is not meant to imply any specific
direction into which such separating occurs, nor does it imply that only
one substrate is moved whereas the other substrate is kept in a fixed
position. Rather, the process of "separating" may imply that one
substrate is moved relative to the other, or it may imply that both
substrates are moved relative to one another, or it may imply that the
other substrate is moved relative to the one substrate. In one embodiment
of such "separating" process, one substrate may simply be lifted from the
other substrate or vice versa.

[0079] Sometimes, in this application, reference is made to positions of a
pattern of metal, metal oxide and/or semiconductor material having metal,
metal oxide and/or semiconductor material present on said first substrate
which "coincide" with positions of a resist pattern where there is no
resist present. Equally, sometimes reference is made to positions of a
pattern of metal, metal oxide and/or semiconductor material having metal,
metal oxide and/or semiconductor material present on a substrate which
"coincide" with positions of a resist pattern where there is resist
present on a substrate. This state of two sets of positions of different
pattern "coinciding" with each other, in its simplest form may mean that
individual positions of the two patterns may have an overlap. In another
embodiment such "coinciding" means that the individual positions within
the pattern of metal, metal oxide and/or semiconductor material are
identical to the positions of the resist pattern where there is resist
present, in which case the pattern of metal, metal oxide and/or
semiconductor material is a positive image of the resist pattern. Or, in
another embodiment it may mean that the individual positions of said
pattern of metal, metal oxide and/or semiconductor material are identical
to the positions of the resist pattern where there is no resist present,
in which case this means that the pattern of metal, metal oxide and/or
semiconductor material is a negative image of the resist pattern.

[0080] In this application, sometimes reference is made to a "first
substrate", a "second substrate" and "a third substrate". The method
according to the present invention, in its simplest form, aims at the
transfer of a pattern of metal, metal oxide and/or semiconductor material
from one substrate to another. In this sense, the "second substrate" may
be considered a "target substrate" onto which said pattern of metal,
metal oxide and/or semiconductor material is to be transferred. Likewise,
if this pattern of metal, metal oxide and/or semiconductor material is
subsequently to be transferred to the "third substrate", such "third
substrate" may be considered the "target substrate". If all three
substrates are involved in the transfer process, i.e. if the pattern of
metal, metal oxide and/or semiconductor material is transferred form the
first substrate via the second substrate to the third substrate, the
second substrate effectively functions as a "shuttle substrate" in that
it serves the purpose of transferring the pattern of metal, metal oxide
and/or semiconductor material from the first substrate to third
substrate.

[0081] The method according to the present invention allows for the
fabrication of patterns of metal, metal oxide and/or semiconductor
material having dimensions which may be as small as ≦10 nm The
method according to the present invention allows the transfer of patterns
where the edge roughness is determined by the edge roughness of the
pattern of metal, metal oxide and/or semiconductor material prepared on
the first substrate. The method according to the present invention
further allows to transfer patterns across step edges. The method
according to the present invention furthermore enables the preparation of
metal contacts on organic layers without the introduction of ad-atoms
into the molecular layer. Thus this methods avoids the introduction of
defects that lead to the formation of filaments during device operation.

[0082] The present inventors have surprisingly found that it is possible
to transfer a metal/metal oxide/semiconductor material pattern which is
the negative or positive image of a resist pattern and thus, in terms of
its dimension is only limited by the dimensions of the resist pattern, to
another substrate using an intermediate shuttle substrate which is
preferably of relatively soft and polymeric nature. The method according
to the can be used for non invasive contacting of organic layers. The
process is scalable and enables the transfer of pattern with dimension
≦20 nm under ambient conditions. The process is easy to perform.

[0083] The inventors have found that by choosing the metal/metal
oxide/semiconductor material and the first substrate in such a manner
that the interaction between these is smaller than the interaction
between metal/metal oxide/semiconductor material pattern and the second
substrate ("shuttle substrate"), a transfer of the pattern from the first
substrate to the second substrate can be achieved, and to subsequent
substrates if the interaction of these subsequent substrates (third
substrate etc.) to the pattern is stronger than the interaction between
the pattern and the second substrate. Alternatively, the respective
interactions can be adjusted by the use of lubricant layers or other
intermediate layers, and/or the use of solvents and/or the use of
solutions to weaken the corresponding interaction.

[0084] The critical dimensions achieved in such a pattern according to the
present invention are only limited by the methodology applied for the
fabrication of the metal/metal oxide/semiconductor material structures on
the surfaces. Since these patterns may be created as a negative or
positive image of a resist pattern, which usually is generated using a
lithographical method, patterns with dimension nm can be achieved.

[0085] Different variations of the shuttle transfer printing process in
accordance with the present invention are described in the following
sections, wherein process 1 describes a process for the transfer of a
metal layer onto a polymer pad as second substrate using a lubricant
layer, while processes 2 to 4 involve no lubricant layer (process 2), the
usage of a polar solvent (process 3) and the usage of a surfactant
solution (process 4).

[0087] The process steps involve the preparation of a resist pattern on a
flat substrate surface (1). Subsequently, a lubricant layer is deposited
onto the substrate (2) before evaporation/deposition of a metal layer (3)
and the lift-off step (4). Such lift-off step in this process and in the
other embodiments of the present invention is performed by dissolving the
resist pattern in an appropriate solvent. This process leads to a
structured metal layer, which is separated from the substrate by a
lubricant layer. The metal layer is brought into conformal contact with a
transfer pad (5), which is typically made from a polymer. If the adhesion
forces of the metal layer on the lubricant layer is weaker than the
interaction between the metal layer and the polymer, the metal layer is
transferred onto the polymer (6).

[0089] The process steps involve the preparation of a resist pattern on a
flat substrate surface (1). Subsequently, the metal is evaporated onto
the substrate (2) before the lift-off step (3). The metal layer is
brought into conformal contact with a polymer pad (4). Since the adhesion
forces of the metal layer on the lubricant layer is weaker than the
interaction between the metal layer and the polymer, the metal layer can
be transferred onto the polymer (5).

[0091] The process steps involve the preparation of a resist pattern on a
flat substrate surface (1). Subsequently, the metal is evaporated onto
the substrate (2) before the lift-off step (3). The metal layer is
brought into conformal contact with a polymer pad (4) and immersed into a
polar solvent (5). The solvent is dragged between the Au layer and the
surface thereby weakening the adhesion forces between the metal layer and
the substrate surface and facilitating the transfer of the metal pattern
onto the polymer pad (6).

[0093] The process steps involve the preparation of a resist pattern on a
flat substrate surface (1). Subsequently, the metal is evaporated onto
the substrate (2) prior to the lift-off step (3). The metal layer is
immersed into a solution containing dithiocarbamate derivatives derived
from primary amines with long alkyl chains (4). The molecules have a
character of a surfactant and also the capability to enter into the space
between the metal layer and the substrate. After a given period of time
the structure is rinsed in water and brought into contact with the
polymer pad (5) for the transfer of the pattern (6).

[0094] From the polymer pad the metal pattern can be finally transferred
onto the target substrate. Prerequisite for this last step is that the
adhesion forces between the metal and the polymer pad is weaker than the
adhesion forces between the metal and the target substrate.

[0095] The target substrate may have functional groups that have a strong
interaction with the metal, be patterned in any way, or have an organic
layer on it, which should provide any functionality, may be covered with
nanowires/nanocolumns, carbon nanotubes (CNTs) etc. or may be solids of
the group of switchable oxides or perovskites.

[0096] Process 5 and 6 describe the transfer of a metal pattern from the
polymer pad onto a Si/SiO2 substrate.

[0097] Process 5:

[0098] The process steps involve a polymer pad with a metal pattern that
was prepared according to any of the processes 1-4 (1). The metal layer
on the polymer pad is wetted with a solvent (e.g. isopropanol, ethanol,
hexane) (2) and brought into conformal contact with a Si/SiO2 substrate
(3). The solvent is dragged between the Au layer and the surface thereby
weakening the adhesion forces between the metal layer and the polymer pad
and facilitating the transfer of the metal pattern onto the Si/SiO2 (4).
(FIG. 2e).

[0099] Process 6:

[0100] The process steps involve the preparation of a resist pattern on a
flat substrate surface (1). Subsequently, a lubricant layer is deposited
onto the substrate (2) before evaporation/deposition of a metal layer (3)
and a lift-off step (4). Subsequently a transfer-mediating layer is
deposited onto the metal layer (5). The transfer-mediating layer/metal
assembly is brought into conformal contact with a polymer pad (6). Since
the adhesion forces of the metal layer on the lubricant layer is weaker
than the interaction between the metal layer/transfer-mediating layer and
transfer-mediating layer/polymer, the metal layer with the
transfer-mediating layer can be transferred onto the polymer (7). The
transfer-mediating layer on the polymer pad is brought into conformal
contact with a Si/SiO2 substrate (8). Subsequently it is immersed in a
solvent (e.g. isopropanol, ethanol, hexane) and the solvent is dragged
between the transfer-mediating layer and the metal surface thereby
weakening the adhesion forces between the metal layer and the polymer pad
and facilitating the transfer of the metal pattern onto the Si/SiO2
substrate (9). At the end the metal patterns are permanently transferred
to the Si/SiO2 substrate (10) (see FIG. 2f).

[0101] Alternatively the transfer pad may be used for the preparation of
flexible organic electronic devices on the piece of polymer.

[0102] The resist pattern can be prepared on single crystalline or
polycrystalline materials, single crystalline or polycrystalline
composite materials such as GaAs, Si, SiO2, Mica, amorphous
composites, such as glass and float glass, and perovskites for example.
For the specific embodiments, SiO2, Mica, and float glass were used.

[0103] The resist pattern can be prepared by optical-, e-beam lithography,
soft lithography, UV-nanoimprint lithography or nanoimprint lithography.
For the specific embodiments the resist patterns were prepared by optical
and e-beam lithography.

[0104] After the resist process, the surfaces may be passivated with a
release layer. For the specific embodiments either no lubricant layer was
used, or 1,1,2,2,-tridecafluoro-octyl)-trichlorosilane was used.

[0105] The transfer pads for the process can generally be made from
elastomers, plastomers, ionomers, and resists. The pads are prepared
either by drop casting and thermal- or photo-induced curing or by hot
embossing techniques. The pads should be fairly smooth and flat. For the
specific embodiments, POP (Affinity VP 8770G) from Dow Chemicals and PDMS
(Sylgard 184, Dow Corning) was used. The transfer pads may be attached to
a hard backplane. The transfer pads maybe chemically modified with a
transfer mediating layer.

[0108] FIGS. 2a)-f) show schematic representations of six different
embodiments of the process according to the present invention,

[0109] FIGS. 3a)-b) show the result obtained by process 1 in accordance
with the present invention, wherein FIG. 3a shows a line of Au,
approximately 100 nm wide, and FIG. 3b shows lines of Au which are 47.8
nm and 50 nm wide, respectively,

[0110] FIG. 4a) shows a microscopic image of a 15 nm Au layer transferred
from SiO2 onto PDMS without a back plane using process 2,

[0111] FIG. 4b) shows a microscopic image of a 15 nm Au layer transferred
from SiO2 onto PDMS with a back plane using process 2,

[0112] FIG. 5 shows an atomic force microscope (AFM) image of a 20 nm Au
layer transferred from Mica onto POP without a back plane using process 3
with a mean surface roughness of 0.5 nm,

[0113]FIG. 6 shows a microscopic image of a 15 nm Au layer transferred
from SiO2 onto POP without a backplane using process 4,

[0114] FIG. 7 shows an optical image of an Au pattern on a PAMMA-G6
modified SiO2 surface using POP as a shuttle substrate ("second
substrate"),

[0115] FIG. 8 shows a scanning electron microscope (SEM) image of a cross
bar structure applied by the method according to the present invention
onto POP,

[0116] FIG. 9 shows a scanning electron microscope image of a cross bar
structure prepared by the method according to the present invention using
POP as a shuttle substrate onto a PAMMAM-G6-modified SiO2 surface,
and

[0119] FIG. 12 shows several traces of an I-V curve of a crossbar
structure in accordance with the present invention. The I-V curve was
measured several times using the same crossbar structure. Different
measurements are shown as different traces. The bottom Au electrodes were
fabricated on substrate 2 according to process 2, a monolayer of 1,4,
benzenedithiol was assembled onto the Au electrodes, and subsequently the
top electrodes were also fabricated according to process 2. The current
is indicated in nano Ampere (nA). The current measured in this device is
5 orders of magnitudes smaller than the current measured in devices
fabricated according to the state of the art. However, the high current
measured in the state of the art devices is indicative of filament
formation due to defects and is a result of the filament formation in the
devices.

[0120] In contrast thereto, the small size of the current measured with a
crossbar structure according to the present invention indicates that the
current is via the molecular layer thus created, and no filaments are
involved which would give rise to significantly higher currents.

[0121] Moreover reference is made to the following examples which are
given to illustrate, not to limit the present invention.

EXAMPLES

[0122] All specific embodiments were performed with Au as metal.

[0123] The transferred patterns were investigated with optical microscopy,
scanning electron microscopy, and atomic force microscopy. Transferred Au
layers were electrically characterized using a probe setup and an
analyzer.

Example 1

[0124] A PMMA resist was spin-coated onto wafer with native oxide and
patterned using electronbeam lithography. After development a descum
plasma treatment was used to clean the trenches. A
perfluoro-alkyltrichlorsilane was vapor deposited onto that wafer. 20 nm
of Au was evaporated at a rate of 8 Å/s onto the wafer at a pressure
of 210-7 mbar. A lift-off was performed using Acetone and
Isopropanol. The patterned Au was transferred onto a freshly prepared POP
pad without backplane (FIG. 3a and b). The background in FIG. 3b is due
to a thin sputtered layer of Au that is required in order to prevent
charging effects during SEM imaging. The lines of Au thus created have
dimensions of ˜50 nm, and the size could be easily reduced to 5-10
nm.

Example 2

[0125] 20 nm of Au was evaporated at a rate of 3 Å/s onto a Si wafer
with a native oxide layer at a pressure of 210-6 mbar. The Au was
transferred onto a freshly prepared PDMS pad without backplane by quickly
detaching the PDMS pad from the SiO2 wafer. The Au layer (FIG. 4a)
shows folding, which result from the flexibility of the PDMS.

Example 3a

[0126] 15 nm of Au was evaporated at a rate of 3 Å/s onto a Si wafer
with a native oxide layer at a pressure of 210-6 mbar. The Au was
transferred onto a freshly prepared PDMS pad attached to a glass
backplane after immersion into isopropanol from the SiO2 wafer onto
the PDMS pad. The Au layer (FIG. 4b) shows some cracks, which result from
the flexibility of the PDMS.

Example 3b

[0127] 20 nm of Au was evaporated at a rate of 3 Å/s onto Mica
substrate at a pressure of 210-6 mbar. The Au was transferred onto a
freshly prepared POP pad with backplane after immersion into water. Water
is dragged between the Mica sheet and the Au layer by capillary forces
and forced the detachment of Au from Mica. The Mica sheet detaches from
the Au layer once the water is dragged fully into the interface between
Au and Mica (FIG. 5).

Example 4

[0128] 15 nm of Au was evaporated at a rate of 3 Å/s onto a glass
substrate at a pressure of 210-6 mbar. The Au was transferred onto a
freshly prepared POP pad without backplane after immersion it for 2.5 h
into a 0.01 M solution of a decyldithiocarbamte sodium salt and rinsing
it with MilliQ water. Subsequently the Au layer is brought into contact
with a thin sheet of POP for the transfer of the Au layer (FIG. 6).

Example 5

[0129] A silicon chip with a 1000 nm SiO2-Layer was immersed into a 1
mM solution of a PAMAM-OS G6 dendrimer in methanol for 5 min and dried
under a stream of Argon. The POP with the patterned gold (prepared
according to Example 1) was pressed onto the PAMAM-OS G6 modified surface
for 2 min. After removing the POP the gold was transferred to the
PAMAM-OS surface. (FIG. 7)

Example 6

[0130] Onto the piece of POP with gold patterns of Example 1 a second
pattern is transferred as described in Example 1 in a way that two
electrodes cross each other in a 90 degree angle and form a crossbar
(FIG. 8).

Example 7

[0131] A PMMA resist was spin-coated onto wafer with native oxide and
patterned using electronbeam lithography. After development a descum
plasma treatment was used to clean the trenches. 20 nm of Au was
evaporated at a rate of 8 Å/s onto the wafer at a pressure of
210-7 mbar. A lift-off was performed using Acetone and Isopropanol.
The chip was immersed into the PAMAM-OS G6 solution in Methanol for 5 min
and dry-blown in Argon. The piece of POP with gold patterns of Example 1
was placed onto this chip in a way, that the two electrodes cross each
other in a 90 degree angle and form a crossbar. The POP was removed and
the second electrodes stayed on the chip (FIG. 9).

Example 8

[0132] 40 nm of Au was evaporated at a rate of 3 Å/s onto a the
patterned Si/SiO2 substrate at a pressure of 210-6 mbar. For the
transfer of the Au pattern onto polyolefine, the polymer was heated to
90° C. and pressed for ˜30 min between two Si/SiO2
wafers. After cooling the POP down to room temperature, the POP is
brought into conformal contact with the Au pattern for the transfer of Au
onto POP 30 μl of Hexane is placed on the POP pad. After 120 sec the
Hexane is evaporated and the POP pad with the Au pattern is brought into
conformal contact with the target Si/SiO2 substrate (FIG. 10). FIG.
10 also shows Au electrodes obtained by conventional optical lithography
for comparison.

Example 9

[0133] 20 nm of Au was evaporated at a rate of 3 Å/s onto a glass
substrate at a pressure of 210-6 mbar. The Au was immersed into a 1
mM mercapto-undecanoicacid in ethanol solution for 5 min, was rinsed with
pure ethanol afterwards and blow dried with nitrogen. The gold was
transferred onto a freshly prepared POP pad without backplane. A piece of
silicon with native oxide was cleaned in sulphuric acid, rinsed in Milli
Q water, and flame annealed. A drop of isopropanol was put onto this
piece. Subsequently the Au layer on the POP is brought into contact with
that piece with the isopropanol. After 1 min the POP is lifted and the
gold stays on the silicon piece. (FIG. 11)

[0145] The features of the present invention disclosed in the
specification, the claims and/or in the accompanying drawings, may, both
separately, and in any combination thereof, be material for realising the
invention in various forms thereof.